STRUCTURE AND ORDERING IN LOCALIZED ADSORPTION OF PARTICLES

Localized, sequential adsorption of colloid particles interacting via screened Coulomb potential was analyzed theoretically and experimentally. The two-dimensional (2D) pair correlation functions were simulated by using the Monte Carlo technique for various surface concentrations θ and for various screening length parameters κα, characterizing the "softness" of the particle-particle interaction potential. For κα ≫ 1 the hard-disk limiting behavior was confirmed (maximum surface concentration θmx = 55%). The θmx for soft disks, which is generally much smaller than the above value, was also determined as a function of the κα parameter. A distinctive tendency toward a short-range ordering, analogous to the 3D results obtaining previously for colloid suspensions, was found for surface concentration close to the θmx value. Theoretical predictions were tested by applying the direct experimental method based on microscope observations of particle adsorption. A monodisperse polystyrene suspension was used (particle size 0.90 μm) and the adsorbing surface was made of mica sheets. Experimental results proved to be in good agreement with Monte Carlo simulations illustrating well the tendency towards structurization (2D quasi-liquid phase formation) for surface concentrations close to the predicted θmx values. © 1990.